A man holds a poster of Kremlin critic Boris Nemtsov, who was shot dead on Friday night, during a march to commemorate him in central Moscow on Mar. 1, 2015. Photo: Reuters/Sergei Karpukhin

The mother of Anna Duritskaya, the Ukrainian girlfriend of murdered Russian politician Boris Nemtsov, is worried that her daughter was “set up” in the opposition leader's killing. Inna Duritskaya said that she has lost touch with her daughter, who is currently under armed guard in Moscow.

Inna claimed that her daughter, a model, was only an eyewitness to the murder and that Russian President Vladimir Putin is trying to link the case to the conflict in eastern Ukraine. Nemtsov, a vocal opponent of Putin's since the latter's election 15 years ago, was gunned down Friday night near the Kremlin in Moscow. The identity of the attackers, who reportedly fired at least seven shots, remains unknown, according to reports.

“I think they want to make her guilty, they want to set her up. What are their reasons to keep her? Everyone knows she had nothing to do with it. I think my daughter is kept because this murder should be linked to Ukraine,” Inna said, according to the Daily Mail, adding: “Somehow I am sure that the task is to link it to Ukraine and she is the only and the easiest way to do so.”

Nemtsov's death triggered a massive rally in Moscow, with thousands pouring out into the city's streets to mourn the dead leader on Monday. The incident also gained international attention, with the U.S. calling for a detailed investigation into Nemtsov’s death.

“The investigators called me and said: ‘You don't worry, she is not a suspect. She is just the main witness. We do not want to let her go because she is the main witness, but you don't worry,’” Inna said, according to the Daily Mail, adding that the night that Nemtsov was murdered Anna was waiting at a restaurant for the Russian opposition leader.

Nemtsov reportedly died after being attacked and shot when the two were returning from dinner.

“Boris became weak and fell down. Anna was very scared, started to call police and then phoned me a minute later. She said: ‘Mama, Boris has been killed. He was shot in his back, he fell down, he is lying here next to me,’” Inna said, according to the Daily Mail. “Next time she called me and said she was in the car and she was being questioned. All night long, until 5 am they were taking her from one police station to another and she was giving her testimony.”

Vadim Prokhorov, Anna’s lawyer in Moscow, claimed, according to the Daily Mail, that Russian authorities did not want the model to return back to Kiev.

“She is ready to come back to Russia if need be but investigators don't want to let her go. As a witness, she is not denied the freedom of movement but actually she is under home arrest. With this in mind, we plan to complain over her illegal custody to the Prosecutor General's Office and the human rights ombudsman,” Prokhorov said, according to the Daily Mail.